ov7670: clean up ov7670_read semantics

Cortland Setlow pointed out a bug in ov7670.c where the result from
ov7670_read() was just being checked for !0, rather than <0.  This made me
realize that ov7670_read's semantics were rather confusing; it both fills
in 'value' with the result, and returns it.  This is goes against general
kernel convention; so rather than fixing callers, let's fix the function.

This makes ov7670_read return <0 in the case of an error, and 0 upon
success. Thus, code like:

res = ov7670_read(...);
if (!res)
	goto error;

..will work properly.
Signed-off-by: Cortland Setlow <csetlow@tower-research.com>
Signed-off-by: Andres Salomon <dilinger@debian.org>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/media/video/ov7670.c

@@ -406,8 +406,10 @@ static int ov7670_read(struct i2c_client *c, unsigned char reg,
 	int ret;
 
 	ret = i2c_smbus_read_byte_data(c, reg);
-	if (ret >= 0)
+	if (ret >= 0) {
 		*value = (unsigned char) ret;
+		ret = 0;
+	}
 	return ret;
 }